<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var age = prompt("请输入你的出生年份:");
        var now = new Date().getFullYear();
        var count = now - age;
        alert("你已经" + count + "岁了！");

    </script>
</body>
</html>